Steam generator



Patented Feb. 27, 1934 UNITED STATES STEAM GENERATOR Walter GustavNoack, Baden, Switzerland, as-

sig'nor to Aktiengesellschaft Brown Boverl &

Cie, Baden, Switzerland, a

of Switzerland joint-stock company Application August 20, 1931, SerialNo. 558,260, and in Germany September 3, 1930 6 Claims.

This invention relates to steam generators and has as its object animproved type of steam generators which, owing to their special workingconditions and construction, smallness in size, weight and watercapacity, no longer form boilers in the accepted meaning of the word,but rather constitute steam generating machines. The chief features ofthese mechanized steam generators are the burning of the fuel mixtureunder high pressure in a pressure resisting combustion chamber, and theexceptionally high velocities at which the combustion gases are passedover the heating surfaces, ensuring small heating surfaces,crossesectional area of the gas passages, and water spaces. As a matterof fact, it hasbeen known for some time that, by increasing the pressureand the velocity, the transmission of heat from a gas to the water to beheated may be considerably improved. In the application to practice,however, the velocity of the heating gases is always kept relativelylow, so that it is hardly likely that steam generators exist in whichvelocities higher than about 25 m/sec., have found application. This, inspite of the fact that scientific research has already extended itsinvestigation into the transmission of heat at higher velocities, sothat, for instance, for elastic fluids (gases), velocities have beenexperimented with up to 100 rn/sec.' However, heretofore no practicalboilers utilizing these velocities were ever built, because theeconomical ,way for obtaining these high velocities was apparent to theart.

I have investigated the behaviour of gases in regard to the transmissionof heat and flow resistance at velocities considerably exceeding thehitherto investigated range and found that by utilizing gas velocitiesof the order of 200 meters per second or more in the neighborhood of thevelocity of the sound, it is possible to economically develop thepressure drop necessary for the generation of these high velocities andproduce steam generators which occupy only a fraction of the space, andhave only a fraction of the weight of boilers of the same capacity madeheretofore. The known laws of heat transmission and resistance to flowdo not apply when a certain velocity is exceeded. If the velocity of thegas amounts to more than one third or one half of the critical speed(velocity of sound at the corresponding pressure and temperature) thenthe flow of gases is no longer similar to the flow of an inflexiblefluid, but properties of the gases become apparent which are caused bythe elasticity (compressibility) of the gas. The

pression of the gas (increase of the potential energy as a result of thedecrease of the kinetic energy).

To obtain these high flow velocities pressure drops are necessary whichamount to one hundred to a thousand times the usual draught met with insteam generators. These high pressure drops cannot be obtained with thesystem of forced draught, as used in ordinary boilers, but specialmeasures must be p o d d for, Several of which I have already describedin previous applications. In the generator of application Serial No.333,345, filed January 18th, 1929, the pressure drop was obtained byprecompressing the fuel mixture and exploding it. The resulting pressureintermittently drives the exhaust gases through the heating tubes. Thispressure drop, however, is only partially converted into high velocity,the remainder of the pressure drop being used to drive a gas turbine,which is cou-- pled to a compressor which delivers the scavenging andcharging air for the combustion chamber. The value of the gas velocityvaries according to the pressure change in the chamber after theexplosion and during the discharge and charging, a.nd alternates betweenapproximately 500 and 200 m/sec.

In the generator of application Serial No. 414,428, filed December 16th,1929, the combustion takes place at constant pressure. The pressure dropto develop the high gas velocities also remains constant just as the gasvelocity, which has a value of between half to full velocity of sound,amounting therefore to at least 200 m/sec. The compressor whichmaintains the pressure drop is driven by a heat engine the heat cycle ofwhich is so coupled with that of the steam generator that all the heatthat is not.utilized for the compression is directed to the steamgenerator for the production of steam.

In the generator of application Serial No. 419,026, filed January 7th,1930, the combustion takes place in the combustion chamber also withconstant pressure, and the heating gases also reach over 200 m/sec. Thecompressor, which develops the pressure in the burner, is driven by agas turbine which is connected to the end of the heat-exchanging ductsand driven by the exhaust gases which acquire their full velocityimmediately on leaving the combustion chamher and are completely oralmost completely cooled before entering the gas-turbine.

The steam generator of the present invention constitutes a further veryadvantageous modification of the above described mechanized steamgenerators. Like the generators referred to above, it comprises apressure resisting combustion chamber, heat-exchange ducts, a gasturbine, and a compressor. The combustion takes place at a constantpressure considerably above atmospheric, which imparts to the gases athigh flow velocity along the heating surface of the ducts. The pressureis maintained by means of a compressor which is coupled with a gasturbine that is driven by the combustion gases. It distinguishes overthe previous constructions by a different consecutive arrangement of theheating spaces and gas turbine as also by a different method ofoperation. The gas turbine is not placed at the end of theheat-exchanging bodies,

but between them and driven by gases which still possess a largequantity of heat, and are comparatively hot. The output of this gasturbine is then so large that it enables operation of the compressorwith a compression ratio which is considerably greater than theexpansion ratio of the gas expanding in the turbine. Large pressuredifferences are thus made available between the delivery end of thecompressor and the inlet duet of the turbine, and between the turbineexhaust and the atmosphere, imparting high velocities to the flow of thegases through the heatexchangers before the turbine, as well as throughthe heat-exchangers after the turbine. These velocities should be atleast V; of the velocity of sound, i. e. at least 150 m/sec., andhigher. The expansion ratio of the gas expanding in the turbine mayamount approximately of the compression ratio in the compressor.

The foregoing and other features and objects of the invention will bebest understood from the following description, reference being made tothe accompanying drawing showing a diagrammatic view of the new steamgenerating system.

It comprises a combustion chamber 101 formed by a pressure resistingcylinder 102, and is closed at the bottom by the inlet header 103 and atthe top by an outlet header 104. The inlet header 103 is shown taperingdown towards the bottom, and mounted therein is a burner 105 to which issupplied combustion air and fuel through the air pipe 106 and the fuelpipe'107. The walls of the cylinder 102 may be made of steel or othermaterial capable of withstanding a high pressure, and are protectedagainst overheating by water tubes 108 extending vertically along thechamber walls and lining same. Around the walls of the inlet header 103thereis a water chamber 110, and around the outlet header 104 is a wateroutlet chamber 111. The water tubes 108 extend between the water inletchamber 110 and the water chamber 111, and permit a rapid circulation ofwater from the lower chamber to the upper chamber. Circulation of thewater is-effected by means of circulating pipes 112 and a pump 113connected between the pipe 114 of the water inlet chamber 110 and theoutlet 1150f the water outlet chamber 111.

The upper portion of the water chamber 111 forms a steam separatorcompartment 116 which is divided from the lower portion of the chamberby a set of blades 117 tending to impart a rotary motion to waterflowing upwards. The water separated from the steam in the portion 116is led directly by a pipe (not shown in the g l W the inlet pipe 112.The top of the steam separator compartment is connected by a pipe oflarge diameter 118 with a relatively small steam collector 119 whichacts as a further steam separator, and into the lower portion of thissteam separator feed-water is injected by a feed-water pump 121 andsupply pipe 120. To the top of the steam collector 119 a steam pipe 122is connected which leads on into a superheater coil 123 mounted in theupper portion of the chamber; the superheated steam passing throughsteam delivery pipe 124 to the steam engines or turbines or otherconsuming apparatus where it is to be used. By a pipe 125 the lowerportion of the steam collector 119 is connected to the circuit of thewater circulating pipe 112, by means of which the water is circulatedthrough the water tubes 108 arranged around the periphery of thecombustion chamber 101.

In the upper end of the inner wall of the header 104, enclosing the topof the combustion chamber, there is a gas outlet chamber 131 havingaround its periphery a set of nozzles 132. To,

these nozzles are connected a set of high-pressure gas discharge ductsin the form of tubes 133 extending downwards through one portion of .the

water tubes 108 disposed around the periphery of the combustion chamber.

The bottom ends of these gas discharge tubes 133 open up into diffusors134 which open into a high-pressure stage gas chamber 135. To the gaschamber 135 there is connected through pipe 136 an inlet to a gasturbine 137 and the outlet end 138 of the gas turbine is connected by apipe 139 to an annular gas discharge duct 140 at the lower end of theinlet header 103. In the top of the gas discharge duct 140 are fittedoutlet nozzles 141 to which are connected a set of low-pressure gasdischarge ducts in the form of tubes 142 extending upwards throughanother portion of the water tubes 108 disposed around the periphery ofthe combustion chamber. The upper. ends of the low-pressure gasdischarge tubes 142 also open up into diffusors 143 which lead into agas outlet duct 144 in the upper-end of the outlet header 104, the gasescaping from the outlet duct through the exhaust pipe 145. The gasturbine 137 is coupled to a compressor 150 which takes in air that hasfirst been passed through an enclosure 151 jacketing the combustionchamber, and its attachments. The compressor takes in the preheated airand delivers it at high pressure through pipe 106 to the burner 105. Afuel pump 152, which may likewise be driven by the gas turbine 137,supplies fuel, such as oil, gas or pulverized fuel through pipe 107 tothe fuel inlet of the burner 105.

The nozzles and blades of the gas turbine are so designed that apressure is created before the turbine which is lower than in thecombustion chamber 101 to the extent of a few metres water col- .umn.This pressure difference is utilized to impart to the gases in theheating tubes 133 a'high velocity of flow in order to obtain a hightrans mission of heat. This high transmission of heat makes it possibleto have comparatively short tubes so that, in spite of high velocitiesof flow, the friction losses due to the tube resistance are relativelysmall. This resistance is further reduced due tothe fact that thecooling of the gases while passing through the tubes 133 and thediffusors 134 causes a compression which counteracts the pressure lossdue to friction in the tubes. The temperature of the gases in the firstheat exchanger (tubes 133) is only diminished to an extent at which thegases still contain sufficient heat energy when arriving at the gasturbine to develop the necessary power for driving the compressor.

The back pressure of the gas turbine must be a few metres water columnabove atmospheric pressure, in order that sumcient pressure is availableto give the gases in the second heat-exchanger (tubes 142) highvelocities. The pressure drop that is available for work in the gasturbine is therefore equal to the pressure developed by the compressorreduced by the pressure losses in. the burner 105 and the sets ofheating tubes 133 and 142.

Since the temperature of the heating gases before the turbine is stillhigh and, in fact. much higher than the final temperature of the airafter the compression the available pressure drop for expansion in theturbine driving the compressor may be made at least 20% lower than thecompression ratio. In order to ensure that the turbine workssatisfactorily at high gas temperatures all gas pipes and blades arecooled by circulating water taken. for instance, from the pipe 112. Thegas turbine and the compressor are independent of the load and thedrives thereof, and may be regulated as desired.

The heat converted into mechanical energy by the gas turbine is takenfrom the gases and is not available for the immediate generation ofsteam. This heat, however, is transferred to the air which is heated bythe compression. The heat energy utilized in compressing the air istherefore almost completely recuperable in the firing of the steamgenerator, and the compression is effected without requiring additionalpower. It is important that no heat is lost from the compressor. Thecompressor should accordingly not be cooled, and the'operation should beadjusted to make it unnecessary to cool the compressor. These conditionsare met by making the charging pressure of the combustion chamberapproximately 2.5 to 3.5 kg/cm absolute. This pressure gives the gasturbine a heat drop that can be expanded in a single turbine wheel. Inoperation, the compressor continuously delivers a combustible charge tothe combustion chamber under a substantial high pressure. The charge issubjected to continuous combustion in the chamber producing therein hotcombustion gases having a pressure head equal to the compressionpressure. Under the action of this pressure head, the combustion gasesare discharged through a set of high-pressure heatexchange ducts, a gasturbine and a set of lowpressure heat-exchange ducts connected in seriesbetween the chamber and the atmosphere. The gas turbine is impelled byan intermediate por- ;ion of the pressure head of the hot combustiongases to drive the compressor with power sumcient to produce therequired charging pressure, the expansion ratio of the gases being 1',or less of the compression ratio of the compressor. A

portion of the pressure head. at the high end before the turbine, isapplied to impart to the combustion gases flowing through thehigh-pressure ducts a high velocity of more than 150 m/sec. to securelarge heat transfer to the surrounding steam generating fluid: andanother portion of the pressure head. at the low end after the turbine,is applied to impart to the combustion gases flowing throughthelow-pressure ducts a high velocity, preferably of more than 150 m/sec.to secure additional large heat transfer to the surrounding steamgenerating fluid. This arrangement utilizes the various pressure andtemperatureranges of the combustion gases in a way which is veryeffective in the steam generation and highly efflcient in producing thepressure for imparting to the gases the high velocity with which thehigh rate of steam generation is secured.

The invention is not limited to the specific details of the methods ofoperation, arrangements, and details of construction referred to inexemplifying and explaining the principles of the invention, and manymodifications and equivalents thereof will suggest themselves to thoseskilled in the art. The terms steam. steam generating fiuid and steamgeneration as used in describing the practical exempliflcations of myinvention refer not only, to steam generated by heating water which ischiefly employed in all vapor power plants at present, but as used inthe specification and claims are intended to include broadly all otherequivalent vaporizable liquids suitable for vaporization by heatconveyed thereto and for utilization as a power medium.

I claim:-

1. The method of generating steam which comprises, initially compressinga gaseous body in a compressor and forming therewith a combustiblecharge of a substantial pressure head, subjecting said charge tocontinuous combustion under pressure. utilizing the upper part of thepressure head of the combustion gases for imparting to them a velocityof the order of one hundred fifty meters per second or more along aheat-exchange surface separating the gases from a steam generating fluidto transfer heat thereto and generate steam, utilizing the next lowerpart of the pressure head of the combustion gases leaving said firstheat-exchange surface for impelling a gas turbine driving saidcompressor and applying the power developed in said gas turbine forinitially compressing said gaseous body, utilizing the remaining part ofthe pressure head of the gases leaving the gas turbine for imparting tosaid gases a velocity above one hundred meters per second along a secondheat-exchange surface separating the gases from a steam generating fluidto transfer thereto remnant heat of the gases, and maintaining theexpansion ratio in the gas turbine sufliciently less than thecompression ratio of the compressor to provide in the combustion gasesbefore and after the turbine pressure drops suficient to impart to saidgases said high velocities.

2. The method of generating steam which comprises, initially compressinga gaseous body in a compressor and forming therewith a combustiblecharge of a substantial pressure head. subjecting said charge tocontinuous combustion under said pressure head, utilizing the upper partof the pressure head of the combustion gases for imparting to them avelocity of the order of one hundred fifty meters per second or morealong a heat-exchange surface separating said gases from a steamgenerating fluid to transfer thereto and generate steam, utilizing thenext lower part of the pressure head of the combustion gases leavingsaid heat-exchange surface for impelling a gas turbine driving saidcompressor and applying the power developed in said gas turbine forinitially compressing said gaseous body, utilizing the remaining part ofthe pressure head of the gases leavingthe gas turbine for imparting tosaid gases a velocity above one hundred meters per second over a secondheat-exchange surface separating said gases from a steam generatingfluid to transfer thereto the remnant heat of the gases, and maintainingthe expansion ratio in the gas turbine at 0.8 or less of the compressionratio of the compressor to provide in the combustion gases before andafter the turbine pressure drops sufficient to impart to said gases saidhigh velocities.

3. The method of generating steam which comprises, initially compressinga gaseous body in a compressor and forming therewith a combustiblecharge of a substantial pressure head, subjecting said charge tocontinuous combustion under said pressure head, utilizing anintermediate part of the pressure head of the combustion gases with anexpansion ratio of 0.8 or less of the compression ratio of thecompressor for impelling a gas turbine driving said compressor, applyingthe power developed in the gas turbine for initially compressing saidgaseous body, and utilizing a sufiicient upper part of the pressure headof the combustion gases before they enter the gas turbine, and asuflicient lower part of the pressure head of the combustion gases afterthey leave the gas turbine for imparting to said combustion gases avelocity of the order of one hundred fifty meters per second or morealong heatexchange ducts that are in contact with a steam generatingfluid to transfer thereto the heat of the gases for steam generation.

4. A vapor generator comprising a pressureproof combustion chamber,means including a compressor for supplying to said chamber a compressedcombustible charge and producing therefrom hot combustion gases of highpressure head having a predetermined range in said chamber,heat-exchange means for holding a vaporizable iquid and having heatingsurfaces constituting a set of ducts having at one end inlet nozzlesconnected to said chamber having a cross section and length proportionedand constructed to apply the upper portion of the pressure head in saidchamber for driving the hot gases from the chamber through said inletnozzles into the ducts at a velocity of about 150 meters per second ormore to heat said liquid and generate vapor, a gas turbine connected inseries with said ducts proportioned and constructed to apply an intermediate portion'of the pressure head of said gases discharged from saidduets with an expansion ratio less than the compression ratio of saidcompressor within said turbine into mechanical power for driving saidcompressor, and additional heat-exchange means for holding a liquidhaving heating surfaces constituting a second set of ducts connected tothe outlet of said gas turbine having a cross section and lengthproportioned and constructed to apply the lower portion of said pressurehead for driving the gases discharged from said gas turbine through theducts at a velocity above 100 meters per second transferring remnantheat thereof to said liquid.

5. A vapor generator comprising a pressureproof combustion chamber,means including a compressor for supplying to said chamber a compressedcombustible charge and producing therefrom hot combustion gases having ahigh pressure head of predetermined range in said chamber, heat-exchangemeans for holding a vapor izable liquid and having heating surfacesconstituting a set of ducts having at one end inlet nozzles connected tosaid chamber having a cross section and length proportioned andconstructed to apply the upper portion of the pressure head in saidchamber for driving the hot gases from the chamber through said inletnozzles into the ducts at a velocity of about 150 meters per second ormore to heat said liquid and generate steam, a gas turbine connectedin'series with said ducts proportioned and constructed to apply anintermediate portion of the pressure head of said gases discharged fromsaid duets with an expansion ratio less than 0.8 of the compressionratio of said compressor within said turbine into mechanical power fordriving said compressor, and additional heat-exchange means for holdinga liquid having heating surfaces constituting a second set of ductshaving inlet nozzles connected to the outlet of said gas turbine havinga cross section and length proportioned and constructed to apply thelower portion of said pressure head for driving the gases dischargedfrom said gas turbine through said inlet nozzles into the ducts at avelocity above 100 meters per second transferring remnant heat thereofto said liquid.

6. A steam generator comprising a pressureproof combustion chamber,means including a compressor for supplying to said chamber a compressedcombustible charge and producing therefrom hot combustion gases having ahigh pressure head of a predetermined range in said chamber,heat-exchange means for holding a steam generating fluid and havingheating surfaces constituting a set of ducts having at one end inletnozzles connected to said chamber having a cross section and lengthproportioned and constructed to apply the pressure head in said chamberfor driving the hot gases from the chamber through said nozzles into theducts at a velocity of about 150 meters per second or more 120 to heatsaid fluid and generate steam, a gas turbine connected in series withsaid ducts proportioned and constructed to apply a portion of the energyof said gases discharged from said ducts within said turbine intomechanical power for 25 driving said compressonand additionalheat-exchange means for holding a. steam generating fluid having heatingsurfaces constituting a second set of ducts having at one end inletnozzles connected to the outlet of said gas turbine hav- 130 ing a crosssection and length proportioned and constructed to apply the energy ofthe gases discharged from said gas turbine for driving said gasesthrough said nozzles into the second set of ducts at a velocity above100 meters per second 135 transferring remnant heat thereof to saidfluid.

WALTER GUSTAV NOACK.

